In reality, whatever seems most comfortable. The higher the ceiling the less it's a big concern, but a rough and ready rule is the lights should be almost 3 feet above the table and the lights need to be 6 feet from the floor.
Something like 5 foot 8 inches or higher the lights need to be, and 2 feet 10 inches away from the pool table. If you got a medium-lowish ceiling then you get out the measuring table and the booklets or the web.
It depends how dim you like it for pool, or if shadows bother you, or one thinks they are getting eyestrain, or maybe the biggest issue, is there a light fixture above that damn pool table to begin with?
The bigger the room and the higher the ceiling, the least stress about table size, and lighting.
A site that's not too technical is: billiardresources.com/billiards-table-lighting.html
I'll quote some of it:
History Of Billiards Table Lighting
Lighting for pool tables has been around since the invention of the game of billiards. The sources for lighting naturally have changed. Very earliest in the game, candles were the main source of light. Those folks lucky enough to have the resources to have a billiard table, would often place the pool table on the top floor so as to take advantage of the natural light from the sunset. In the late 1840’s, kerosene lamps came along, this was the primary source of light until the light bulb was invented.
Three Important Functions of Pool and Billiards Table Lighting
How Much Lighting Is Required for your Pool Table?
- Lights the pool table evenly
- Eliminates shadows created by the pool balls
- Illumination minimizes eye fatigue
What Kind of Lighting Is Best for a Pool Table?
- 8 foot pool table requires 310 watts
- 9 foot pool table requires 400 watts
Where is the Best place to hang a Light Above a Pool Table?
- Lights Should Be Diffused,not Spot or Flood Lights
- Halogen Lights Are Not A Good Choice as they create too much eye Strain
- A Pool Table light should be centered exactly over the table.
- A Light Can Be hung from 33-36 inches (your own personal preference) above the slate of the table.
- To easily figure this, the standard height of a BCA spec table is 31 inches from the floor. Add 31 inches plus 33-36 inches and you will have where the bottom of the light should be.